Field of the Invention
The invention relates to correcting and/or preventing errors during the measurement of coordinates of a work piece. In particular, the invention relates to an arrangement for measuring coordinates of a work piece, a method for producing such an arrangement and a method for operating such an arrangement.
Coordinates of a work piece can be specified and measured in different ways. By way of example, the coordinates relate to a reference system, for example what is known as the laboratory system or the coordinate system relating to the work piece or a work piece holder. However, it is also possible, for example, that dimensions of the work piece are registered and specified, which dimensions relate to at least two reference points of the work piece, e.g. a length, a width or a diameter. In order to determine the coordinates, coordinate measuring machines (also abbreviated CMM in the following) or the users of the coordinate measuring machines are dependent on knowing the position and, often, also the alignment of a probe for sensing the work piece, and also the position and alignment of the work piece itself, or at least knowing a possible change in the position and alignment. A change in the position and alignment can occur, in particular, if work piece and probe are moved relative to one another in order to be able to undertake further measurements of the coordinates. Therefore, if different parts of an arrangement for measuring coordinates of a work piece are mobile relative to one another, corresponding movements can lead to errors when measuring the coordinates of the work piece. Examples of such relative movements are rotational movements of a rotational device (this is the subject matter of a first aspect of the present invention), movements when setting the position and/or alignment of a probe or probe head (which has a sensor system) for sensing the work piece for the purposes of determining the coordinates (this is the subject matter of a second aspect of the present invention) and the mechanical bending due to mechanical forces and/or the thermal expansion or thermal contraction of the material of an arrangement for measuring coordinates or of a machine tool (this is the subject matter of a third aspect of the present invention).
All this mobility is given in addition to the movement of an optionally present probe, which movement the probe performs during the measurement of the coordinates of a work piece by mechanical sensing (i.e. while the probe contacts the work piece). In particular, such probes which are deflected from a neutral position during mechanical sensing of the work piece due to the mechanical forces acting between work piece and probe, wherein the deflection is established and evaluated for the purposes of determining the coordinates of the contact point, are known. The additional mobility therefore leads to errors when measuring the coordinates.